Cancel one dependant's contracts within a contract bundle. Based on the provided date, the system determines the closest date on which coverage can end: coverage always ends on the 14th or on the last day of a month. The date must be in the future and on or before the end of coverage. The rest of the bundle stays active. The planholder cannot be cancelled individually — cancelling the planholder ends the whole bundle, so use the contract bundle cancellation endpoint for that.